1. Field of the Invention
The present invention relates to a refrigerator oil composition. More precisely, it relates to a refrigerator oil composition containing a refrigerant that comprises carbon dioxide (CO2) as the essential component, and to a method of using the composition for lubrication especially in a compression refrigeration cycle equipped with an oil separator and/or a hot gas line.
2. Description of the Related Art
In general, a compression refrigeration cycle for refrigerators, for example, that for compression refrigerators comprising a compressor, a condenser, an expansion valve and an evaporator is of a closed system in which is circulated a mixed liquid comprising a refrigerant and a lubricating oil. In compression refrigerators of that type, in general, chlorofluorocarbons such as dichlorodifluoromethane (R-12) and chlorodifluoromethane (R-22) have heretofore been used as refrigerants. Various types of lubricating oils have been produced and used together with such refrigerants. However, when released in air, these Flon compounds that have heretofore been used as refrigerants will bring about environmental pollution, as destroying the ozone layer existing in the stratosphere. Therefore, their use is being severely controlled in all the world. Given the situation, new refrigerants, hydrogen-containing Flon compounds such as hydrofluorocarbons and hydrochlorofluorocarbons have become specifically noted. Hydrogen-containing Flon compounds, especially hydrofluorocarbons such as typically 1,1,1,2-tetrafluoroethane (R-134a) will not destroy the ozone layer. However, as their life in air is long, they will cause global warming. Therefore, the recent tendency in the art is toward using refrigerants from natural resources that are free from the problem.
Above all, carbon dioxide (CO2) is excellent as it is harmless to the environment and is safe to human beings. In addition, it has the advantages of (1) appropriate pressure near to the optimum pressure in economical aspects, (2) extremely small pressure ratio as compared with other conventional refrigerants, (3) good compatibility with ordinary oil and with construction materials for machines, (4) anywhere easy availability, and (5) extremely low costs with no necessity for recovery. However, using such CO2 as a refrigerant is often problematic in that, when it is combined with ordinary refrigerator lubricating oil, the oil composition has poor lubricity and its ability to improve the abrasion resistance of machine parts is poor. As a result, the machine parts being lubricated with the oil composition will become unstable and could not keep long-term durability. In addition, the system in which is used CO2 requires higher jetting pressure, as compared with that where is used R-134a or the like, with the result that the viscosity of the lubricating oil therein is lowered and the sealability of system will be worsened.
The present invention has been made in consideration of the viewpoints noted above, and its object is to provide a refrigerator oil composition, which exhibits good lubricity and sealability in compression refrigeration cycles where is used a refrigerant comprising CO2 as the essential component, and which can be stably used for a long period of time, and also to provide a method of using the composition for lubrication.
We, the present inventors have assiduously studied and, as a result, have found that the object of the invention can be effectively attained by using a lubricating oil composition comprising a specific lubricating oil base and an additive. On the basis of this finding, the inventors have completed the present invention.
Specifically, the invention provides the following:
1. A refrigerator oil composition comprising a refrigerant that comprises carbon dioxide (CO2) as the essential component, and an ester-based lubricating oil composition; wherein the ratio of refrigerant/lubricating oil composition falls between 99/1 and 10/90 by weight.
2. The refrigerator oil composition of above 1, wherein the ester-based lubricating oil composition comprises a base oil that comprises an ester oil as the essential component and has a kinematic viscosity at 100xc2x0 C. of from 5.5 to 30 mm2/sec, and from 0.005 to 5% by weight, relative to the base oil, of at least one selected from extreme pressure agents and acid scavengers.
3. A method of using the refrigerator oil composition of above 2 in a compression refrigeration cycle equipped with at least one selected from oil separators and hot gas lines.
4. A method of lubricating a compression refrigeration cycle equipped with at least one selected from oil separators and hot gas lines, for which is used the refrigerator oil composition of above 2.
5. The refrigerator oil composition of above 1, wherein the ester-based lubricating oil composition comprises a base oil that comprises an ester oil as the essential component and has a kinematic viscosity at 40xc2x0 C. of from 56 to 130 mm2/sec, and wherein the ester oil is of an ester compound of pentaerythritol with at least one selected from C8 and C9 fatty acids.
6. The refrigerator oil composition of above 5, wherein the ester oil is of a carbonate compound.
7. A method of using the refrigerator oil composition of above 5 in a compression refrigeration cycle equipped with at least one selected from oil separators and hot gas lines.
8. A method of lubricating a compression refrigeration cycle equipped with at least one selected from oil separators and hot gas lines, for which is used the refrigerator oil composition of above 5.
9. The refrigerator oil composition of above 5, wherein the fatty acids are in the form of a mixed acid of a branched C8 fatty acid and a branched C9 fatty acid.
10. A method of using the refrigerator oil composition of above 9 in a compression refrigeration cycle equipped with at least one selected from oil separators and hot gas lines.
11. A method of lubricating a compression refrigeration cycle equipped with at least one selected from oil separators and hot gas lines, for which is used the refrigerator oil composition of above 9.